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Questions 2.5.2(a)

  1. Which of the Period 3 elements react by losing electrons? Explain your answer.
  2. Which of the Period 3 elements react by gaining electrons? Explain your answer.
  3. Identify the element that reacts but is not likely to gain or lose electrons. Explain your answer.
  4. Name the stable element, that does not react at all. Why is it unreactive?
    For the three metals sodium to aluminium, first ionization energy and reactivity depend on the ease with which their outermost electrons can be knocked off. First ionization energy is the amount of energy required to remove an electron from a neutral atom.
  5. Which of the three elements is expected to have the lowest first ionization energy? Explain your answer.
  6. Identify the least reactive element of the three. Explain your answer.
  7. Write the formulae of ions formed when sodium, magnesium and aluminium lose all their outermost electrons.
  8. How does ionic radius vary from sodium to aluminium?
  9. Write the valencies of all the elements in Period 3.
  10. Describe the change in valency as we move from sodium to argon?


Answers to Questions 2.5.2(a)

  1. Sodium, magnesium and aluminium. They have 1 to 3 outer electrons, which require less energy to lose than gain 7 to 5 and achieve the stable noble gas configuration.
  2. Phosphorus, sulphur and to chlorine. They have 7 outermost electrons which require much more energy to lose than gaining 1 to achieve the stable noble gas configuration.
  3. Silicon. Its outer energy level is half-filled with 4 electrons. Gaining and losing 4 electrons to achieve the stable configuration require nearly the same amount of energy.
  4. Argon. It already has a stable noble gas configuration.
  5. Sodium (Na). It has the largest atomic radius; therefore its outer electron is farthest from the nucleus and requires the least energy to knock off.
  6. Aluminium (Al). It has the smallest atomic radius of the three. Therefore its outermost electrons are close to the nucleus
    7. and strongly held by it. Moreover, it has more (3) electrons to lose and this requires more energy.
  7. Na+, Mg2+, Al3+
  8. Ionic radius becomes smaller because of the increasing nuclear charge (11+ to 13+) that draws electrons closer to the nucleus.
  9. 1, 2, 3, 4, 3, 2, 1, 0.
  10. Valency increases from 1 to 4 then decreases to 0.